Hydrogenation and dehydrogenation of hydrocarbons are important reactions in the refining and petrochemical industries. Non-limiting examples of such reactions include reforming, dewaxing, hydrocracking, hydrotreating and hydrofinishing. Many such reactions employ a catalyst comprising a noble metal component deposited on a support composed of a porous crystalline material combined with an amorphous binder.
Currently, most noble metal catalysts are made by impregnating platinum and/or palladium complexes onto the catalyst support. The catalyst is then dried to remove water and calcined in air to decompose the metal complexes leaving behind highly dispersed platinum and/or palladium oxides on the support surface. The catalyst is then activated by reducing the noble metal oxides in the presence of hydrogen to produce active platinum and palladium sites. However, during both catalyst activation (particularly in the presence of water vapor) and on-stream operation, the catalytic activity declines due to metal sintering which occurs when finely dispersed platinum and palladium particles agglomerate and the active metals surface is reduced.
The present invention seeks to address this problem by providing a novel method of adding noble metal anchors onto the surface of the catalyst support via pre-treatment and thereby reducing the propensity for metal sintering and significantly improving catalyst stability. While improving stability, adding noble metal anchors appears to have no measurable negative effect on initial catalyst activity or selectivity.
U.S. Pat. No. 5,041,401 discloses a zeolite catalyst composition comprising (a) a zeolite component, (b), a non-framework multivalent metal oxide component occupying the pores of the zeolite, said non-framework multivalent metal oxide being incorporated into the pores of the zeolite component by a method which includes calcining at a temperature of at least about 600° C. in an atmosphere containing from about 1 to 100 parts per million of water, and (c) a noble metal component. The presence of the metal oxide component (b) is said to impart significantly increased resistance to agglomeration and/or migration of the noble metal component (c) in operation, but incorporating the metal oxide in the pores of the zeolite is expected to change the activity and selectivity of the finished catalyst.
In an article entitled “Effect of aluminum modification on catalytic performance of Pt supported on MCM-41 for thiophene hydrosulfurization” in Applied Catalysis A: General 308 (2006), pages 111-118, Kanda et al. disclose that alumina modification of MCM-41 improves the Pt dispersion and catalytic activity of a Pt/MCM-41 hydrodesulfurization catalyst. There is, however, no disclosure or suggestion in this article that aluminum modification would increase the agglomeration resistance of a noble metal deposited on a bound MCM-41 catalyst.